1. Field of the Invention
Embodiments of the present invention generally relate to high capacity energy storage device and energy storage device components, and more specifically, to a system and method for fabricating such high capacity energy storage devices and storage device components using processes that form three-dimensional porous structures.
2. Description of the Related Art
High-capacity energy storage devices, such as lithium-ion (Li-ion) batteries, are used in a growing number of applications, including portable electronics, medical, transportation, grid-connected large energy storage, renewable energy storage, and uninterruptible power supply (UPS).
A transformation of Li-ion battery (LIB) volume manufacturing technology is necessary to achieve successful commercialization of vehicle electrification. Significant progress is needed to address technical performance, reliability, manufacturing cost requirements, and industrial engineering for Gigawatt Hour (GWh) scale factories.
A lithium ion battery is a highly integrated device with many elements that all have to be engineered to achieve design and production targets. Typically, the Li-ion battery cell elements include cathode and anode electrodes, insulated by a porous separator saturated in a liquid electrolyte in a package with contacts. The cathode material layer may be bound to an aluminum (Al) current collector and an anode material layer is bound to a copper (Cu) current collector. Current collector thickness is determined by manufacturing transport constraints rather than cell resistance contribution, the separator provides electrical isolation of the anode and the cathode while preventing physical shorting and has sufficient porosity for lithium ion conductivity.
Contemporary cathode electrode materials include particles of lithium transition metal oxides bonded together using polymer binders with conductive fillers such as carbon black. The most widely used binder is the Polyvinylidene Fluoride (PVDF). Electrodes are formed by slot die coating with a slurry mixture of active materials, binder, and carbon black dispersed in the most common organic solvent for PVDF, N-Methylpyrrolidone (NMP) which requires elaborate volatile organic compound (VOC) capture equipment. The electrode is subsequently dried, with the dryer often being 40 to 70 meters long due to the slow rate needed to prevent cracking of the electrode. A calendering step is used to compress the electrode to increase the electrical connections among active materials, conductive additives, and current collector as well as to increase the volumetric energy density by adjusting the porosity.
The contemporary anode electrode is either graphite or hard carbon. Similar to the cathode, the anode binder is typically PVDF to bond the particles together and conductive additives such as carbon black are sometime added to the anode mix as well to improve power performance.
While graphite or carbon based anodes have established themselves as the anode of choice in current generation batteries, they do fall short of meeting the requirements for the next generation. This is mainly due to the lower energy density (375 mAh/g) of graphite and the fact that the state-of-the-art graphite is near its theoretical limit.
Hence there has been a lot of interest in the industry in exploring alternate anode materials that would have much higher energy density and enhanced safety while remaining low cost and retaining long cycle life. High capacity alloy anodes such as silicon and tin have been explored as potential replacements for graphite due to their large theoretical energy densities. However, these materials have not been transformed to high volume manufacturing. There are three main technical limitations that have deterred the adoption these advanced materials using conventional slurry based approaches.
First, the large volumetric stress that occurs in these alloy anodes during lithiation/delithiation leads to the pulverization of alloy anode particles resulting in poor cycle life. Second, the poor or unstable solid electrolyte interphase (SEI) layer formed on the surface leads to instability in performance and also to potential safety issues. Third, the first-cycle irreversible capacity loss is too high in these alloy anodes to be introduced to practical application.
One way to circumvent some of these issues, if not all, is to engineer particles that embed the alloy anodes in multiphase composites or by particle size engineering. These approaches, while moderately successful in mitigating the first cycle loss and extending the cycle life, fail to achieve desired gravimetric and volumetric energy densities due to the mass contribution from inactive components. Improvements in energy density, often if not always, result in a corresponding decline in power density.
Accordingly, there is a need in the art for faster charging, higher capacity energy storage devices that are smaller, lighter, and can be more cost effectively manufactured.